 
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   cmr.spatial.mbr.Mbr
+
+  (coordinate-system
+    [_]
+    :cartesian)
 
   (mbr [br] br)
 

  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  cmr.spatial.geodetic_ring.GeodeticRing

  (mbr
    [ring]
    (:mbr ring))

(defprotocol SpatialRelations
  "Defines functions for determining relations between different spatial areas."

  (coordinate-system
    [shape]
    "Returns the coordinate system of a shape if it has one. Points do not occupy
    a set coordinate system.")

  (mbr [shape] "Returns the minimum bounding rectangle of the shape")

  (contains-north-pole? [shape] "Returns true if the shape contains the north pole")
